There are a wide variety of imaging systems available for recording all or substantially all of a spherical field of view.
One example of such an imaging system is a dual hemispherical lens system, in which two image sensors each having a 180 degree field of view are arranged in opposition to one another. The images from each sensor can then be combined to generate an image representing the entire spherical field of view. Such systems tend to suffer from high distortion.
The amount of distortion can be reduced by increasing the number of individual image sensors, although this generally increases the cost and complexity of both the imaging system itself as well as the subsequent image processing. This is because more image sensors are required and this in turn results in increased amounts of data needing to be processed to combine the individual images.
The Ladybug® brand imaging systems offered by Point Grey Research Inc., having an address at 12051 Riverside Way, Richmond, BC, Canada, V6W 1K7 use six image sensors, with five spaced-apart image sensors arranged to point outwardly from a common ring and one image sensor arranged to point axially relative the ring. However, these image sensors do not capture the entire spherical field of view.
Another type of imaging system is based on the geometry of a dodecahedron. One embodiment of this type of imaging system uses image sensors arranged to point outward from the faces of a dodecahedral housing. Such a system is described in U.S. Pat. No. 5,023,725 to McCutchen. A subsequent patent to McCutchen, U.S. Pat. No. 6,141,034 teaches another embodiment of a dodecahedral imaging system which uses divided lenses in a tetrahedral lens mount with criss-cross optics, with each image sensor recording three pentagons surrounding a single dodecahedral vertex. The divided lens system and criss-cross optics may increase the risk of misalignment between the lens system components and the cameras.
Moreover, many of the methods used to merge individual images together to represent a spherical field of view are subject to distortion because they must correlate pixel positions on a planar image with positions on a curved spherical surface.